Why use a manifold?

[IndySam]

Originally Posted by GeeTwo

Based on some number crunching I did during build this year, it appeared that the fastest cylinder performance would be to have a large tank (at least twice and preferably three times as large as the cylinder capacity) on the working pressure side of the regulator, then feeding directly from the tank to the solenoid valve to the cylinder. We did not get to test this, as it turned out the valves we were using had much too low a cv for this to make a difference.

I can tell you from experience this is true. This is how we plumed our soccer ball kicker on our Breakaway bot and it made a big difference.

[IndySam]

The other reason to use a manifold is the exhaust air exiting through the manifold makes a cool sound.

[ollien]

Originally Posted by GeeTwo

Based on some number crunching I did during build this year, it appeared that the fastest cylinder performance would be to have a large tank (at least twice and preferably three times as large as the cylinder capacity) on the working pressure side of the regulator, then feeding directly from the tank to the solenoid valve to the cylinder. We did not get to test this, as it turned out the valves we were using had much too low a cv for this to make a difference.

Is there a reason for this? I had heard this once our season ended and I was annoyed that we hadn't tried it to fix our shooter.

[GeeTwo]

Originally Posted by IndySam

I can tell you from experience this is true. This is how we plumed our soccer ball kicker on our Breakaway bot and it made a big difference.

Always good to know that the math gave the right answer!

Originally Posted by ollien

Is there a reason for this? I had heard this once our season ended and I was annoyed that we hadn't tried it to fix our shooter.

Essentially, the air on the working side of the regulator is already there, ready to work. The air on the high side has to filter its way through the pressure regulator, which is not as fast. The tank needs to be significantly larger than the working piston so that there is not too much pressure drop in the supply during the stroke.

Also note that if you are going for a fast stroke, your cylinder should be large enough to move the load (slowly) at a rather low pressure, somewhere around 35psi/(desired acceleration + gravity), with acceleration measured in gees. There will be around 20 psi drop going through the solenoid valve, and pressure reduction as the cylinder extends (or retracts); the remainder is F=ma. (I am assuming here that your fast stroke is for the purpose of working against gravity to throw a ball or other object.)

[Michael Hill]

Originally Posted by IndySam

The other reason to use a manifold is the exhaust air exiting through the manifold makes a cool sound.

Truth. Coolness of sound is, by far, the most accurate figure of merit for any FIRST robot.

[FrankJ]

A little of topic but. Bimba, a great supporter of First and is also is sort of the standard of the cylinders that we use has published a handbook on pneumatic design. Sizing of cylinders included.

[tr6scott]

Just to confirm GeeTwo and IndySam,

Attached is a photo of our 2014 Robot, where we used two pneumatic cylinders to shoot the ball.

This shot is a little blury due to the camera DOF at the solenoids, but if you look closely and follow the tubing, you will see that the output of the solenoid, there is about a 1" of tube ported directly to the cylinder. The opposite end of the cylinder was left open to atmosphere.

On the input end of the solenoid, you will see about a 6" piece of tubing, to the bottom of a storage tank. This was a dedicated low "working" pressure storage tank for the solenoid and cylinder. With his set up we were able to shoot just with pneumatics, and also be able to shoot back to back shots, needed for out two ball autonomous.

https://youtu.be/IOU_eZ6CrqI

[adciv]

On our 2014 robot we used a pneumatic catapult. We ended up putting a large number of tanks on the working pressure side to assist. We also ended the season with higher CV solenoids than we started with due to performance issues.

One key thing we did was we started logging air pressure on the 120psi side, the working pressure (nominally 60), and at the piston. Key things we learned.
1) The regulator suffers from hysteresis and does not always return to the set point every time.
2) We could have a 30psi or greater pressure differential across the solenoid.

I may still have the data available if anyone is interested.